Variable cavity resonator



NOV. 4, 1952 A, v, HAEFF ET AL 2,616,966

VARIABLE CAVITY RESONATOR Filed July 50, 1948 ZZ/IIEEIT lhhhlllllalllnllllhllll I "l I l l n l n a 0 1:! IT E l m/ j 1 A 23 23 28 29 I8 I 32 INVENTORS \J ANDREW V. HA EFF BY THURE E. HANLEY ATTORNEY Patented Nov. 4, 1952 VARIABLE "CAVITY RESONATOR Andrew Haefi, Washington, D. fi and Thure E. Hanley, Temple Hills, Md.

Original application Januaryll, 1946,'Serial No. 640,636. "Divided and this application :Iuly "30, 1948, SerialNo'.41;6'44

8 Claims.v (Cl. 1 7'844) (Granted under the act of March 3, 1883, as

amended April 30, 1928'; 370 0. 'G. 757

This application is a division of application .Serial 'No. 640,636, filed January 7111, 1946, now

Patent .No. 2,589,248.

Thislinvention relates to electrical 's1gnalgenerators and more particularly to high frequency generators adapted to operate in a microwave region. x r

In .therm'icrcwave regions of the frequency spections as a "frequency determining element for a source of oscillation energy, typically a velocity modulation electron tube. In such an oscillation generator, energy is supplied to'the resonant cavity-structure at the resonant frequency thereof, or at a frequency bearing some harmonic relationship to the resonant frequency. In the oscillator structures heretofore available, it was not possible to tune the resonant cavity to produce sustained oscillations at any particular .fre quency throughout a wide band of frequencies simply by the alteration of a single cavity dimension because, at certain frequency points in the wide band, effects existed which prevented operation entirely or which rendered operation unsatisfactory because of low output; for example.

Accordingly, it is an object of the present invention to provide an oscillation generating system employing a, cavity resonator as a fre: quency selective element which is tunable to any particular frequency over a wide band of frequencies without unsatisfactory operation occurring at any frequency in the band.

Another object is to provide a cavity resonator constructed in such a manner so that two dimensions thereof may be simultaneously .adjusted to control the resonant frequency thereof.

Still another object of the present invention is to provide a cavity resonator of substantially \rectangularcross section in which the widthand .len'gth dimensions thereof may be simultaneously adjusted to control the resonant frequency.

Other objects and features of the present invention will become vapparent upon consideration of the following detailed description "in connectionwiththe accompanying drawing which illustrates one embodiment of th'einvention. "It is to be expressly understood, however, that the drawing is designed for purposes of illustration only and not as a definition of the limits of the invention, reference for the latter purpose'being had to the appended claims.

In the drawing, wherein similar reference characters denote similar elements throughout the similar views:

- 2 Fig. l is va schematic drawing of a velocity modulation oscillator employing a resonant cavity as a frequency selective element;

'Fig. 2 is a sectional illustration of an-oscillator and cayity assembly constructed in accordance with the principles of the present invention, and

Fig. 3 is a sectional illustration through line "3'-'3 :o'f'Fig.2.

According to the fundamental concepts of the present invention, an oscillator assembly employing *a velocity modulation tube and a resonant cavity is rendered tunable to any particular frequency ina wide frequency band by simultaneous alteration of two dimensions of the resonant cavity and by controlling the potential applied to an element or elements of the velocity modulation tube,

.A schematic illustration of a resonant cavity velocity modulated high frequency signal generator is depicted in Fig. 1. The generator includes a resonant cavity in formed partly within and partly without the glass envelope of tube I, connectio'ns between the inner and outer parts of the cavity being made through annular con- 'ductive rings lZ and I13 sealed to the glass walls .of the tube J I Electrons emitted by the cathode structure M of 'th'etube I travel in the direction of electrode l5 maintained at a voltage positive with respect to the voltage of the cathode structure M. In their passage from the cathode structure M to the positive electrode 15, the electrons .are subjected to various fields from the cylindrical electrodes "I16 and fl 1, and the annular rings l2 and 3. The combined action of the foregoing fields concentrates the electrons into a small diameter beam and transfers .a part of the beam energyftothe resonant cavity ill. The oscillation generator functions .in a manner similar to conventional. velocity modulation oscillators with celectronfbunching taking ,place in the so-called fdri;ft space between the rings l2 and J3 to produce and sustain oscillations. .A part Of the ener y generated within the oscillator is supplied to !'an external power consuming device, not shown,"by'means of .an output coupling arrangement and coaxial transmission line I 8..

Provision .is made in the oscillator generator forflmodul'ating theoutput signal bya beam control electrode or grid structure i9. By adjust- ;mentlof the potential erence existing between the grid structure 19 and the cathode M, (by means oflpotentiometer .20, the number .of electravelling from (the cathode 1'4 to the electrode' 1'5 lmay be controlled to alter the amplitude of the oscillatory field within the resonant cavity l and hence the amplitude of the output signal.

The frequency of the output signal is determined primarily by the dimensions of the cavity H] and the potential difference existing between the elements I4 and I5 of the tube ll, because either factor will alter the bunching of electrons which occurs in passage thereof between the annular rings l2 and I3.

A sectional view of a resonant cavity'embodying the principles of the present invention is shown in Fig. 2. The resonant cavity is constructed around the oscillator tube II and comprises an outer cavity bounded in the plane of Fig. 2 by plates 20, 2|, 22 and 23, and by the annular rings 2 and 3. A slidable assembly 24 divides the outer cavity to form a variable size resonant cavity for the high frequency oscillator bounded by the plates 20, 2| and 23, theannular rings I2 and I3, and the slidable assembly 24.

Construction of the resonant cavity structure which allows simultaneous adjustment, of two dimensions thereof will be more fully understood with reference to Fig. 3 of the drawing. As shown, the resonant cavity is furtherbo'unded in the plane of the figure by slidable wall members 25 and 26. The members 25 and 26 are positionally variable and may be moved in opposite directions, either simultaneously or separably, by means of threaded shafts 21 and 28, respectively. The shafts 27 and 28 are tunable simultaneously through gearing 29, 30, 3| and 32, and a countershaft 33. The shaft 33 may be rotated directly by control knob 34, or indirectly through other shaft members if desired for convenience of adjustment. When it is desired to' position the members 25 and 26 individually, a clutch device 3-5 is operated to disconnect the gear 32 from the shaft 28, and the latter shaft is then rotatable independently of the shaft 21 by a control knob 36. The lower surface of the assembly 24 rests upon the upper surface of the slidable members 25 and 26 as shown in'the drawing, and is held in the position disclosed by guide members 3! and 38 and associated springs 39 and 40. The assembly 24 is provided with ace'ntral portion 4| having a lower surface substantially perpendicular to the slidable members 25 and 26, and with two outer portions 42 and 43 inclined in opposite directions toward the plate 23. With as oscillation generator employing a cavity resonator as a frequency selective element thereof with the cavity resonator constructed in such a manner so that two dimensions thereof may be simultaneously adjusted to determine the resonant frequency thereof. An oscillator generator including a cavity resonatorembodying the principles of the present invention is capable of providing sustained oscillations at any particular frequency throughout a wide bandof frequencies without disadvantageously effecting operation of the generator. I

Although only one embodiment of the present invention has been disclosed and described herein it is to be expressly understood that various changes and substitutions may be made therein without departing from the spirit of the invention as well understood by those skilled in the art. Reference therefore will be had to the appended claims for a definition of the limits of the invention.

' The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties j thereon or therefor.

.50 this arrangement, motion of the members 25 and What is claimed is:

1.'An electrical resonator comprising a plurality of fixed wall portions and a plurality of movable wall portions arranged to form a substantially closed resonant cavity structure, means diametrically mounting a pair of said movable wall portions in sliding contact with said fixed wall portions for movement in a first direction parallel to the planes of the fixed wall portions for establishing one dimension of said cavity structure, means mounting another of said movable wall portions in sliding contact with a pair of said fixed wall portions for movement in a direction substantially perpendicular to said first direction to establish another dimension of said cavity structure. means maintaining sliding contact between said another movable wall and said pair of movable wall portions and means responsive to movement of said pair of movable wall portions for moving said another movable wall portion in accordance therewith.

2. An electrical resonator comprising a plurality of wall portions forming a substantially closed three-dimensional resonant cavity structure, means slidably mounting one of said portions for movement relative to the other of said portions in a first direction to establish one dimension of the cavity structure, means slidably mounting another of said portions in quadrature with respect to said one portion for movement relative to the remainder of said other portions and said one portion in a direction different from said first direction to establish another dimension of the cavity structure, means comprising a clutch member operable to selectively move said one portion, and means comprising a cam member associated with said another portion engageable by said one portion for moving said another portion in accordance with movement of said one portion.

3. An electrical cavity resonator structure comprising a first pair of diametrically positioned walls spaced by a third wall determining one dimension of the cavity structure, a second pair of diametrically positioned walls movably mounted in sliding contact with said first pair of walls and said third wall in a direction perpendicular to said first dimension to determine a second dimension of the cavity structure, and a fourth wall mounted in sliding contact with the first pair of walls in a direction perpendicular to said first and said second dimensions to determine a third dimension of the cavity structure, said fourth wall including a pair of surfaces oppositely inclined in the direction of the second dimension to maintain sliding engagement with the second pair of walls.

4. A three-dimensional cavity resonator comprising three fixed wall members forming the bottom and a first pair of opposite sides of said resonator, a pair of oppositely disposed movable wall members slidably engaging said fixed wall members and forming a second pair of opposite sides of said resonator, a third movable wall memher forming the top of said resonator, said third movable wall member having inclined portions slidably engaged by said pair of movable wall members, means engaging said movable pair of wall members to vary the space therebetween, thereby simultaneously causing the distance between the movable top and fixed bottom to vary.

5. A three-dimensional cavity resonator substantially parallelepiped in shape comprising three fixed wall members forming the bottom and a first pair of opposite sides of said resonator, a pair of oppositely disposed movable wall members slidably engaging said fixed wall members and forming a second pair of opposite sides of said resonator, a third movable wall member forming the top of said resonator, said third movable wall member having inclined portions slidably engaged by said pair of movable wall members, means engaging said movable pair of wall members to vary the space therebetween, thereby simultaneously causing the distance between the movable top and fixed bottom to vary.

6. A three-dimensional cavity resonator comprising three fixed walls forming the bottom and a first pair of opposite sides of said resonator, a pair of oppositely disposed movable Walls slidably engaging said fixed Walls and forming a second pair of opposite sides of said resonator, a third movable wall having at least one inclined extension slidably engagable with said pair of oppositely disposed movable walls to form a movable top of said resonator, and means comprising a rotatable member for simultaneously varying the distance between said pair of movable walls in one direction thereby varying the distance between the movable top and fixed bottom in another direction.

7. A three-dimensional cavity resonator substantially parallelepiped in shape comprising three fixed rectangular shaped walls forming the bottom and a first pair of opposite sides of said resonator, a pair of oppositely disposed movable walls slidably engaging said fixed walls and forming a second pair of opposite sides of said resonator, a third movable wall having at least one inclined extension slidably engageable with said pair of oppositely disposed movable walls to form a movable top of said resonator, and means comprising a rotatable member for simultaneously varying the distance between said pair of movable walls in one direction thereby varying the distance between the movable top and fixed bottom in another direction.

8. A three-dimensional cavity resonator comprising three fixed wall elements, a pair of oppositely disposed movable wall elements slidably engaging said fixed wall elements, a third movable wall element slidably engaging said pair of movable wall elements, means comprising a rotatable element for varying the distance between the pair of oppositely disposed movable wall elements in one dimension and means slidably engaging said pair of movable wall elements, said means comprising a cam element associated with said third movable wall element for varying the distance between the third movable wall element and one of said fixed wall elements in a second direction.

ANDREW V. HAEFF. THURE E. HANLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,158,493 Brailsford et al. May 16, 1939 2,410,109 Schelleng Oct. 29, 1946 2,460,090 Kannenberg Jan. 25, 1949 2,473,777 Beechlyn June 21, 1949 2,514,678 Southworth July 11, 1950 2,567,748 White Sept. 11, 1951 FOREIGN PATENTS Number Country Date 905,624 France Dec. 10, 1945 

